# Digital Image Processing Questions and Answers – Basic Grey Level Transformation

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This set of Digital Image Processing Multiple Choice Questions & Answers (MCQs) focuses on “Basic Grey Level Transformation”.

1. Using gray-level transformation, the basic function linearity deals with which of the following transformation?
a) log and inverse-log transformations
b) negative and identity transformations
c) nth and nth root transformations
d) All of the mentioned

Explanation: For Image Enhancement gray-level transformation shows three basic function that are:
Linearity for negative and identity transformation
Logarithmic for log and inverse-log transformation, and
Power-law for nth and nth root transformations.

2. Using gray-level transformation, the basic function Logarithmic deals with which of the following transformation?
a) Log and inverse-log transformations
b) Negative and identity transformations
c) nth and nth root transformations
d) All of the mentioned

Explanation: For Image Enhancement gray-level transformation shows three basic function that are:
Linearity for negative and identity transformation
Logarithmic for log and inverse-log transformation, and
Power-law for nth and nth root transformations.

3. Using gray-level transformation, the basic function power-law deals with which of the following transformation?
a) log and inverse-log transformations
b) negative and identity transformations
c) nth and nth root transformations
d) all of the mentioned

Explanation: For Image Enhancement gray-level transformation shows three basic function that are:
Linearity for negative and identity transformation
Logarithmic for log and inverse-log transformation, and
Power-law for nth and nth root transformations.

4. If r be the gray-level of image before processing and s after processing then which expression defines the negative transformation, for the gray-level in the range [0, L-1]?
a) s = L – 1 – r
b) s = crᵞ, c and ᵞ are positive constants
c) s = c log (1 + r), c is a constant and r ≥ 0
d) none of the mentioned

Explanation: The expression for negative transformation is given as: s = L – 1 – r.

5. If r be the gray-level of image before processing and s after processing then which expression helps to obtain the negative of an image for the gray-level in the range [0, L-1]?
a) s = L – 1 – r
b) s = crᵞ, c and ᵞ are positive constants
c) s = c log (1 + r), c is a constant and r ≥ 0
d) none of the mentioned

Explanation: The expression for log transformation is given as: s = c log (1 + r), c is a constant and r ≥ 0.

6. If r be the gray-level of image before processing and s after processing then which expression defines the power-law transformation, for the gray-level in the range [0, L-1]?
a) s = L – 1 – r
b) s = crᵞ, c and ᵞ are positive constants
c) s = c log (1 + r), c is a constant and r ≥ 0
d) none of the mentioned

Explanation: The expression for power-law transformation is given as: s = crᵞ, c and ᵞ are positive constants.

7. Which of the following transformations is particularly well suited for enhancing an image with white and gray detail embedded in dark regions of the image, especially when there is more black area in the image.
a) Log transformations
b) Power-law transformations
c) Negative transformations
d) None of the mentioned

Explanation: Negative transformation reverses the intensity levels in the image and produces an equivalent photographic negative. So, well suited for the above given condition.

8. Which of the following transformations expands the value of dark pixels while the higher-level values are being compressed?
a) Log transformations
b) Inverse-log transformations
c) Negative transformations
d) None of the mentioned

Explanation: Log transformation derives a narrow range of gray-level values in input image to wider range of gray-levels in the output image, and does performs the above given transformation.
The inverse-log is applied for the opposite.

9. Although power-law transformations are considered more versatile than log transformations for compressing of gray-levels in an image, then, how is log transformations advantageous over power-law transformations?
a) The log transformation compresses the dynamic range of images
b) The log transformations reverses the intensity levels in the images
c) All of the mentioned
d) None of the mentioned

Explanation: For compressing gray-levels in an image, power-law transformation is more versatile than log transformation, but log transformation has an important characteristics of compressing dynamic ranges of pixels having a large variation of values.

10. A typical Fourier Spectrum with spectrum value ranging from 0 to 106, which of the following transformation is better to apply.
a) Log transformations
b) Power-law transformations
c) Negative transformations
d) None of the mentioned

Explanation: The log transformation compresses the dynamic range of images and so the given range turns to 0 to approx. 7, which is easily displayable with 8-bit display.

11. The power-law transformation is given as: s = crᵞ, c and ᵞ are positive constants, and r is the gray-level of image before processing and s after processing. Then, for what value of c and ᵞ does power-law transformation becomes identity transformation?
a) c = 1 and ᵞ < 1
b) c = 1 and ᵞ > 1
c) c = -1 and ᵞ = 0
d) c = ᵞ = 1

Explanation: For c = ᵞ = 1 the power-law transformations s = crᵞ become s = r that is an identity transformations.

12. What is gamma correction?
a) A process to remove power-law transformation response phenomena
b) A process to remove log transformation response phenomena
c) A process to correct log transformation response phenomena
d) A process to correct power-law transformation response phenomena

Explanation: The exponent used in power-law transformation is called gamma. So, using the ᵞ value, either ᵞ < 1 or ᵞ> 1, various responses are obtained.

13. Which of the following transformation is used cathode ray tube (CRT) devices?
a) Log transformations
b) Power-law transformations
c) Negative transformations
d) None of the mentioned

Explanation: The CRT devices has a power function relation between intensity and volt response.
In such devices output appears darker than input. So, gamma correction is a must in this case.

14. Log transformation is generally used in which of the following device(s)?
a) Cathode ray tube
b) Scanners and printers
c) All of the mentioned
d) None of the mentioned

Explanation: All the mentioned devices uses gamma correction and so power-law transformation is generally of use in such case.

15. The power-law transformation is given as: s = crᵞ, c and ᵞ are positive constants, and r is the gray-level of image before processing and s after processing. What happens if we increase the gamma value from 0.3 to 0.7?
a) The contrast increases and the detail increases
b) The contrast decreases and the detail decreases
c) The contrast increases and the detail decreases
d) The contrast decreases and the detail increases

Explanation: In power-law transformation as gamma decreases is increase in image details however, the contrast reduces.

Sanfoundry Global Education & Learning Series – Digital Image Processing.

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